Television in natural color



y 14, 1940- R. LORENZEN 2.200.285

TELEVISION IN NATURAL COLOR Filed June 22, 1937 S Sheets-Sheet l 49 4FIG.4 V Z 45 45m :3

44 wgm m No.2 F165 .5

l6 ,5 la 50 56 FIGS 5 6 7 F166 45 44 I ATTORNEY.

May 14, 1940.

TO AMPLIFIER FIG.8

T0 AMPLIFIER FIG.'7

ELECTRON BEAM R. LORENZEN 2.200.285

TELEVISION IN NATURAL COLOR Filed June 22, 1937 3 Sheets-Sheet 2 FIGFIC;.9

INVENTOR. Z EN.

ROBERT LOR ATTORNEY.

R. LORENZEN TELEVISION IN NATURAL COLOR Filed June 22 1937 FIG. 12. 96/

0 10a lo I 8 9 6 b l0 x N06 N FIG-.13.

O O 0 I a y I 8 by!" l 3 \\\gl7 INVENTOR. kosurr 1.0mm 2 EN.

ATTORNEY.

3 Sheets-Sheet 3 Patented May 14, 1940 UNITED STATES PATENT OFFICTELEVISION 1N NATURAL COLOR Application June 22, 1937, Serial No.149,562

12 Claims.

The present invention relates to improvements in television in naturalcolors.

One of the objects of the invention is the provision of special cathoderay oscillographs for the purpose of receiving colored televisionimages.

Another object of the present invention is the provision of specialphotoelectric transmitting tubes for the purpose of transmitting coloredtelevision images.

Still another object of the present invention is the provision of acathode ray oscillograph wherein the glass face is colored for thepurpose of using it as a color filter, thereby effecting an economy byeliminating separate or external color filters.

Still another object of the present invention is to provide a threecolor screen in conjlmction with a single beam cathode ray tube, so thatthe three color eifect is produced with a single beam.

Fig. 1 represents a longitudinal section through a modified cathode raytube using only one set (two pairs) of deflecting electrodes, andemploying the primary color method.

Fig. 2 represents the shape of the scanning wave employed in thereception of pictures on the cathode ray tube shown in Fig. 1.

,Fig. 3 represents the fluorescent screen employed in the cathode raytube shown in Fig. 1.

Fig. 4 represents a longitudinal section of a modified cathode ray tubewherein deflection is accomplished by one set (two pairs) of deflectingelectrodes and using the complementary color method.

Fig. 5 represents the shape of the scanning wave employed in the cathoderay tube shown in Fig. 4.

Fig. 6 represents the fiuorescent'screen of the tube shown in Fig. 4.

Fig. 7 represents a sectional view of a portion of a photoelectrictransmitting tube adapted for the transmission of television pictures incolor, in which three kinds of photoelectric materials are used, eachbeing most sensitive to that portion of the spectrum corresponding toeach of the three primary colors.

Fig. 8 differs from Fig. '7 mainly insofar as a single photoelectricmaterial is used. this photoelectric material being approximately equalin sensitivity throughout the visible spectrum.

Fig. 9 represents a perspective view of a photoelectric face of aphotoelectric transmitting tube whereby the wave forms shown in Fig. 2and Fig. 5 are obtained when three photoelectric transmitting tubes ortwo photoelectric transmitting tubes are used respectively.

Fig. 10 represents a longitudinal view of a photoelectric transmittingtube showing how the internal conductive coating can be arranged whenthree separate photoelectric transmitting tubes are used for thetelevision transmission of colored pictures.

Figs. 11, 12, and 13 show the position of the electron beams for thephotoelectric transmitting tubes actuated by red, green, and blue forparts l5, l5, and I1 of the scanning wave of Fig. 2.

Referring to Fig. 1, the cathode ray tube i has an electron emittingcathode 2. These electrons are modulated in accordance with the signalintensity in any of a number oi. methods known to the art, butpreferably by means of a grid It. The electrons pass through theaperture of a centrally apertured anode 3. The electron beam is thensubjected to the two scanning fields due to the varying potentials onthe" two pairs of deflecting plates 4 which are in a relation ofquadrature. The electron beam then impinges upon the fluorescent screenor screens 5, 6, l, which emits light proportional in intensity to themodulating signal.

The novel features of the fluorescent screen 5, 5, I can be understoodby reference to Fig. 1 and Fig. 3. There are two major methods ofutilizing this fluorescent screen for the reception of coloredtelevision pictures.

In the first method, the fluorescent screen may be divided into threeapproximately equal areas such as 5, G, and 1. Each of these areas isgiven a coating of fluorescent material such that each area respectivelyemits a light of each of the three primary colors: red, green, and blue.For example. area 5 may be given a coating of zinc phosphate which emitsa red fluorescence, area 6 may be given a coating of zinc silicate whichemits a green fluorescence, and area I may be coated with calciumtungstate which emits a blue fluorescence. Any other suitablefluorescent materials may be used. The images on screens 5, 6, and I arefocussed by means of lenses ll, l2, and I3 respectively, or by any othersuitable optical system, upon the viewing screen It in such a. mannerthat the three images are exactly superimposed. Due to the practicaldifficulties in obtaining fluorescent materials which fiuoresceatexactly the desired spectral frequencies, and also at just the rightintensity, it is desirable to interpose a red color filter 8 betweenscreen 5 and lens ii, a green color filter 9 between screen 6 and lensl2, and a blue color filter i0 between screen I and lens l3. Theinterposition of properly designed color filters will result not only ina delimitation of the frequency of the light to the exact portion of thespectrum desired, but also in a correction of the intensity of the lightfrom each of the three screens so that a proper color and intensitybalance is obtained. vThe phosphorescent afterglow of each fluorescentscreen should be as nearly the same as possible in order to avoiddistortion of the picture appearing on the viewing screen l4.

vIn the second method, screens 5, 6, and 1 are coated with the samefluorescent'substance. In this case the fluorescent material should beof such a nature as to emit white light, or, at least approximate tothis condition by emitting light in each of the spectrum bandscorresponding to the three primary colors. This condition can befrequency, or both, of the fluorescent screen.

After passing through red filter 8, green filter 9, and blue filter III,the light from the three filters is focussed by means of lenses ll, l2,and I3 respectively, such lenses being so arranged as to superimpose thethree images upon the viewing screen l4. What was intended to convey atthis point was a well known optical arrangement, where the centerpicture is projected by means of an ordinary lens to a centrally focusedpoint, while the two outer pictures were focused upon the same focalpoint through the medium of two prisms, one to each picture. It isthought that this arrangement is so well known as not to needillustration. By this arrangement chromatic dispersion is not ofimportance since each of the three images are emitting approximatelymonochromatic light.

Of the various types of scanning waves which might be employed in theoperation of the cathode ray tube of Fig. 1, the recommended type is thesaw-tooth wave as shown in Fig. 2. Section l5 of the line is operativeover section 5 of the fluorescent screen, portion iii of the line isoperative over portion 6 of the screen, and part I! is operative overpart I of the screen. Line l8 represents the return of the beam to thebeginning of screen 5, the beam now being ready to again sweep thefluorescent screen 5, B. 1 but a line lower. The method whereby thetransmitter produces such a scanning wave will be described in anothersection of this specification.

Fig. 4 represents a modified cathode ray tube which differs from Fig. 1only insofar as the fluorescent screen is now divided into two partsinstead of three, and that the principle of operation is based upon theuse of complementary colors rather than primary colors. The cathode raytube 38 contains a filament 39 which emits electrons. These electronsare modulated by the incoming signal by means of grid 4|, and then passthrough an aperture in the anode 40. The electron beam is then subjectedto the influence of a set of deflecting plates 42. The electron beam inconsequence traces a pattern on fluorescent screens 33 and 44. Theoperation of the fluorescent screens 43 and 44 will be understood byreference to Fig. 4 and Fig. 6. There are two principal methods ofdesigning the fluorescent screens 43 and 44 for the reception of coloredtelevision pictures.

In the first method the fluorescent screen may be divided into twoapproximately equal areas such-as 43 and 44. Each of these areas isgiven a coating of fluorescent material such that each area respectivelyemits a light of one of a pair of complementary colors. For example.area 43 may be given a coating of zinc phosphate which emits a redfluorescence, and area 44 may be given a coating of zinc silicate whichemits a green fluorescence. Any other pair of complementary colors maybe used as well as any other suitable fluorescent materials. -The imageson screens 43 and 44 are focussed by means of lenses 4! and 48respectively, or by any other suitable optical system, upon the viewingscreen 49 in such a manner that the two images are exactly superimposed.Due to the practical dimculties in obtaining fluorescent materials whichfluoresce at exactly the desired spectral frequencies and also at justthe right intensity it is desirable to interpose a red color filter45between screen 43 and lens 41, and a green color filter 46 betweenscreen 44 and lens 49. The interposition of properly designed colorfilters will result not only in a delimitation of the fre: quency of thelight to the exact portion of the spectrum desired but also in acorrection of the intensity of the light from each of the two screens sothat a proper color and intensity balance is obtained. Thephosphorescent afterglow of each fluorescent screen should be as nearlythe same as possible to avoid distortion of the picture appearing on theviewing screen 49.

In the second method, screens 43 and 44 are coated with the samefluorescent substance. In

this case the fluorescent material should be of such a nature as to emitwhite light, or else to emit in each of the complementary color spectralbands. The red color filter 45 and the green color filter 46, in theevent that these are the pair of complementary colors chosen, serve notonly to pass red and green light respectively, but also serve tocompensate for deviations both as regards spectral frequency, orintensity of the particular spectral frequencies, or both, of thefluorescent screen. After passing through red filter 45 and green filter46, the light from the two filters is 'focussed by means of lenses 4!and 43 Of the various types of scanning waves which might be employed inthe operation of the cathode ray tube of Fig. 4, the recommended type isthe saw-tooth wave shown in Fig. 5. Section 50 of the line is operativeover section 43 of the fluorescent screen and portion 5| is operativeover portion 44 of the fluorescent screen. Line 53 represents the returnof the beam to the beginning of screen 43, the beam now being ready toagain sweep the fluorescent screen 43, 44, but a line lower. The methodwhereby the transmitter produces a scanning wave of this type will bedescribed in another section of this description.

It lies within the scope of this invention to have any number of suchcolored or uncolored areas and also that regardless of number of areasthese areas are not limited either as regards the 'use of complementaryor primary colors but may be of any desired color or combination ofcolors.

is not limited to any particular shape of fluorescent screen or shape ofcathode ray. tube.

It should be further understood that although deflecting plates havebeen used as a means of producing the scanning waves, that suchlimitation is not intended, as any other well known deflecting means maybe employed, such as defleeting coils, or a combination of deflectingcoils and plates.

Furthermore, the present invention is not limited to use with cathoderay tubes .only, but

1 may also be used in conjunction with tubes of any type in which theray can be electrically deflected.

The viewing screen may be either opaque or translucent and may, ineither event, be colored, if it be found that further color correctionof the picture is desirable.

Furthermore, for certain applications of the present invention, there isnot intended a limitation, where the phrase primary colors is used,merely to the physicists primary colors (red, green, blue), but there isalso claimed as within the scope of the invention the use of thepainters primary colors (red, yellow, blue).

In Fig. 7 there is shown part of a special photo-electric transmittingtube. The image of the object to be televised in color is separatelyfocussed by means of lenses 65, 6B, and 81 upon the three photoelectricsurfaces 12,14, and 15. These three photoelectric areas 12, I4, and 15are respectively approximately selectively sensitive to the threeprimary colors red, green, and blue; so that the electric charges builtup in the photoelectric condenser II will be for each ele mental pointof 12 proportional to the intensity of the red in the light 13 falling,on eachelemental point of 12, and the amount of green in the light I3falling on 14, and the amount of blue in the light falling on 15. Thephotoelectric surfaces 12, 14, and 15 are separated from the metal plate11 by an insulator l6. Eachof the minute photoelectric globules of 12,H, and I emits electrons, the number of which is proportional to theintensity of light falling thereon. This causes an electric stressbetween surfaces 12, H, 15 and the conductor TI. The electron beam 80sweeps these photoelectric globules line by line and discharges eachminute condenser, thereby resulting in a minute variation of currentbetween metal plate 11 and the cathode of the electron gun.Consequently, an impedance II connected across the cathode of theelectron gun and metal plate Tl will have potential variations set upacross its terminals. The grid and cathode of an amplifying tube 19 canbe connected to the terminals of this impedance and the potentialvariations are then amplified. If

the electron beam scans the photoelectric surface i in the order red,green, blue, there will be produced the line l5, l6, i! of Fig. 2. Inview of the 'difliculty of getting the photoelectric materials torespond sharply and selectively to exactly the three spectralfrequencies required, it is advisable to use color filters 68, i9, andIII, which pass red, green, and blue respectively. These filters may beplaced either before or after the focussing lenses 65, 66, 61. Thesefilters can, moreover, be so designed so as to compensate also forinequalities in electronic emissiveness of the three photoelectricsurfaces.

In the event that the complementary color method is used the onlychanges required are the reduction of lenses, filters, and photoelectricsurfaces from three to two. The two color filters and the twophotoelectric surfaces are now responsive to each of a pair ofcomplementary colors, say red and green. Then if each line scans firstred and then green, the line 50, 5| of Fig. 6 is produced.

In Fig. 8 the only change made is the substitution of a uniformphotoelectric surface 88 to re ,place the three photoelectric surfaces12, II, 15.

In this figure similar parts to that shown in Fig. I are primed. Thephotoelectric material should be approximately equally sensitive to allcolors, particularly-to red, green, and blue. Inequality of sensitivityto the three primary colors can be compensated for by a proper design offilters 82, 83, and 84. Light from the object to be televised in naturalcolors passes through the red filter 82, the green filter l3, and theblue filter 84, and is focussed by lenses 85, 8G and 81 upon the threeseparate areas of photoelectric surfaces 88. The operation of Fig. 8 isfrom this point on identical with that given for Fig. 'l.

To use the method of Fig. 8 for the complementary color method it ismerely necessary to substitute two filters of complementary colors forthe three primary colored filters of Fig. 8.

Fig. 9 represents a perspective view of the photoelectric condenser of aphotoelectric transmitting tube, where the surface of photoelectricglobules 89 is separated from the metal plate 9! by an insulating film90. The novel feature of the invention is the conductive strip 92 whichis connected to the cathode of the electron gun, or to the internalconductive coating of the photoelectric transmitting tube, or to ground,depending on the circuit arrangement used. Asthe conductive strip 92 ofFig. 9 will function exactly as the internal conductive coating I06 ofFig. a detailed description will not be given.

Fig. 10 represents a longitudinal view of a photoelectric transmittingtube 93 which contains an electron emitting cathode 94. Electrons passthrough an aperture in the anode 95 thereby resulting in an electronbeam Hill which is subjected to an electric field by the two paralleldeflecting plates 96 and 91, and to an electromagnetic field by the twocoils 98 and 99. Light from an object I03 passes through a color filterill and thence through a lens ")5 which focusses the image of object 103upon the photoelectric surface' I08 which is composed of a large numberof minute photoelectric globules. The photoelectric surface :08 isseparated by an insulating film II!!! from a metal plate III! whichlatter is connected to the grid of an amplifying tube. The electron beamI00 is subjected to the electric and electromagnetic scanning fields andbecomes either electron ray [ill which scans the photoelectric surfacesI08, or else either of the electron rays I02 which falls upon theconductive coating I06 which is connected to the ground II". Thedeflecting fields are so biased or regulated, as to cause, in the caseof the primary color method of colored television, the electronic beamIII toscan the photoelectric surface for. one third of the'length of asingle complete scanning line, and beam I02 to fall upon the conductivecoating for two-thirds of the length of a single complete scanning line.Consider three tubes R, G, and B of the type shown in Fig. together withtheir respective associated equipment, and also consider the scanningwave shown in Fig, 2. Say that photoelectric transmitting tube R isactuated by red light, tube G by green light, and tube B by blue light.Represent the electronic beam of tube R by 1', that of tube G by a, and

that of tube B by b. Then, in Figs. 11, 12, audit, the small letters r.g, b corresponding to the electronic beams of the photoelectrictransmitting tubes respectively actuated by red, green, and blue. willbe followed by the numerals 15, I 6, or I I depending upon which part ofthe scanning line of Fig. 2 is influencing the ray. Thus, in Fig. 11, rl5 represents the middle point of the scanning line I 5 of Fig. 2. InFigs, 11, 12, and l3,

the photoelectric surface is represented by I08, and the internalconductive coating by I06. It will be seen from an inspection of Figs.11, 12, and 13 that the ray of each of the three tubes is scanning thephotoelectric surface for onethird of a scanning line. Line l8 of Fig. 2represents the return sweep to start a new scanning line.

The application of this technique to color television by thecomplementary color method requires merely the use of two photoelectrictransmitting tubes actuated by a-pair of complementary colors, insteadof the three tubes actuated by primary colors as described above.

Although throughout this description therehave been described methods ofscanning by first scanning a line in the order red, green, blue, itremains within the scope of this invention to scan the images in anyorder of colors, andalso, if desired, to scan completely a whole picturein the red, then the whole picture in the green. and then the wholepicture of the blue.

This invention is not limited to'the particular embodiment described,but may be variously scope of the invention. Furthermore, although inthe description, the scanning wave used was of the saw-tooth type, it isnotintended to limit the scope of the invention only to saw-toothscanning, as other types of scanning waves may be employed.

It is further understood that the photoelectric transmitting tubesdescribed were merely illustrative, and that it lies within the scope ofthe claims to apply the principles herein disclosed to other types ofsuch tubes.

Thus there have been described various means for transmitting andreceiving television images in natural colors.

What is claimed is:

1. In a television system, means for receiving television images innatural colors, including a single cathode 'ray oscillograph comprisinga cathode, a single modulating electrode, an anode, deflecting devices,and a fluorescent screen divided into three distinct and separate areassuch that one of these areas emits light of one of the primary colors, asecond area emits light of a second primary color, and the third areaemits light of the third primary color whereby the entire screen isscanned by a single cathode ray beam.

2. In a television system, means for receiving television images innatural colors, including a single cathode ray oscillograph comprising acathode, a single modulating electrode, an anode, deflecting devices,and a uniformly coatedfluorescent screen capable of emitting light ineach of the spectralbands of the three primary colors, the colorseparation being effected by three independent and separate colorfilters and being acted upon by a single cathode ray beam.

3. In a television system, means for receiving television images innatural colors, including a single cathode ray oscillograph comprising acathode, three separate modulating electrodes,

an anode, three separate sets of deflecting devices, and three separateand distinct fluorescent screens, one of the three screens being capableof emitting light of one of the primary colors, a second screen to'asecond primary color, and a third screen of the third primary color.

4. In a television system, m for receiving television images in naturalcolo including a single cathode ray oscillograph comprising a.

cathode, a single modulating electrode, an anode, deflecting devices,and a fluorescent screen divided into two separate and distinct areassuch that one of these areas emits light oh one of a means of separateand distinct color filters which are acted upon by a single cathode raybeam.

6. In a television system, means for receiving television images innatural colors, including a single cathode ray oscillograph comprising acathode, two separate modulating electrodes. an

anode, two separate sets of deflecting devices, and modified withoutdeparting from the spirit and two separate and distinct fluorescentscreens, one of the two screens being capable of emitting light of oneof a. pair of complementary colors, and the other screen of the other ofthe pair of complementary colors.

7. In a television system adapted for receiving television images innatural colors and including a single cathode ray oscillograph havingthe image reproducing face thereof divided into three separate anddistinct areas, such that the image reproducing face of each of theseseparate areas is differently colored, each area being colored tocorrespond to each of the three primary colors, said screen being actedupon by only a single beam from the oscillograph.

8. In a television system adapted for receiving television images innatural colors and including a single cathode ray oscillograph havingthe image reproducing face thereof divided into two separate anddistinct areas, such that the image reproducing face of each of theseseparateareas is differently colored, each area being colored tocorrespond to each of a pair ofcomplementary colors, said screen beingacted upon by only a combination a single photoelectric transmittingtube, the photoelectric surface of which. tube has a uniformphotosensitive surface which is responsive to each of the three primarycolors, and

aaoopss 5,

combination a single photoelectric transmitting tube, the photoelectricsurface of which has a uniform photosensitive surface which isresponsive to each of the two colors of a pair of com- 1 plemen'tarycolors, and two separate and distinct 5 color filters for effectingcolor separation.

ROBERT LORENZEN.

